RUDDER TRIALS, U. S. S. STERETT. 303 



Performance on Rudder Trials, June g, igii. 



Maximum speed 28.6 knots. 



Draught (mean during trials) 9 ft. ^ in. 



Corresponding displacement (trim i in. by head 



at beginning, 7 in. by stern at end) 835 tons. 



Depth of water 12 to 20 fathoms. 



The type of rudder with dimensions and necessary data for computation 

 is given on Fig. i, Plate iii. The general arrangement of steering gear, 

 showing recording dynamometer, is given on Fig. 2, Plate 11 1. 



RECORDING DYNAMOMETER. 



A vertical spring dynamometer was inserted in the standing part of the 

 port tiller chain. The deflection of the spring, which was a measure of the 

 tension in the chain, was communicated by a suitable multiplying device 

 to a fountain pen which traced on a moving strip of paper a continuous 

 force curve. The dynamometer is indicated in Fig. 2, Plate 112, and shown 

 in detail in Fig. 3, Plate 113, and in Plates 115, 116, and 117. A detailed 

 description of dynamometer is given in Appendix I. The chronograph or 

 recording device is shown in Fig. 4, Plate 114, and Plates 115, 116, and 117, 

 and a description is given in Appendix II. 



Before being installed on board ship, the dynamometer was calibrated 

 by subjecting it to known tensile forces in a 150,000-lb. tensile testing 

 machine. In Fig. 8, Plate 118, are shown calibration curves for five springs. 

 The average deviation of the experimental points from the curves is less than 

 i.o per cent of the maximum force applied. A detailed description of the 

 method of calibration is given in Appendix III. 



FRICTION TESTS. 



Tests were made both in dry-dock and afloat to determine the friction 

 of the steering gear. The ship was first placed in dry-dock, the mid-position 

 of the rudder accurately established as described in Appendix IV, the 

 special helm-angle indicator set up, and the dynamometer inserted in the port 

 tiller chain (Fig. 2, Plate 112). The helm was repeatedly moved back and 

 forth by power, and a continuous record obtained of the tension in the chain! 

 The following day, similar tests were made with the ship moored alongside 

 a pier. The analysis of the tests and the method of applying a correction 

 for friction to the results of the turning trials subsequently made, are given 

 in Appendix V. 



